Turkey on Sunday accused Germany of supporting the network of a U.S.-based Muslim cleric it blames for last year’s attempted coup, comments likely to aggravate a diplomatic feud between the two countries.

Germany and Turkey have been locked in a deepening row after Berlin banned some Turkish ministers from speaking to rallies of expatriate Turks ahead of a referendum next month, citing public safety concerns.

On Saturday, German news magazine Der Spiegel published an interview with the head of Germany’s BND foreign intelligence agency, who said Ankara had failed to convince it that the cleric Fethullah Gulen was responsible for the coup attempt.

“Turkey has tried to convince us of that at every level but so far it has not succeeded,” Bruno Kahl was quoted as saying.

President Tayyip Erdogan’s spokesman said Kahl’s comments were proof Germany was supporting Gulen’s network, which Ankara refers to as the “Gulenist Terrorist Organisation” or “FETO”.

“It’s an effort to invalidate all the information we have given them on FETO. It’s a sign of their support for FETO,” Ibrahim Kalin told broadcaster CNN Turk.

Turkish President Tayyip Erdogan makes a speech during a meeting in Istanbul, Turkey, March 19, 2017. REUTERS/Murad Sezer

“Why are they protecting them? Because these are useful instruments for Germany to use against Turkey.”

There was no response from Germany to the comments.

Ankara blames Gulen’s network of followers in the military for the abortive putsch in July, when a group of rogue soldiers seized tanks, helicopters and war planes to attack parliament and attempt to overthrow the government. More than 240 people were killed in the coup attempt.

Gulen, a former Erdogan ally who has lived in self-imposed exile in the United States since 1999, has denied the charges and condemned the coup.

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Kalin said there was a possibility Erdogan could plan a rally to address Turks in Germany before the April 16 referendum on changing the constitution, a move that would further heighten tensions with Berlin.

The constitutional change would give Erdogan sweeping new powers. Critics say it would give him too much power.

At a speech on Sunday in Istanbul, Erdogan lashed out against a Turkish-German journalist now in jail in Turkey, calling him a terrorist agent.

Erdogan, who was speaking at a meeting of an Islamic foundation, said the reporter, Deniz Yucel of Germany’s Die Welt newspaper, would be tried by Turkey’s independent judiciary.

Authorities arrested Yucel, a dual Turkish and German national, last month on charges of propaganda in support of a terrorist organization and inciting the public to violence.

He was initially detained after he reported on emails that a leftist hacker collective had purportedly obtained from the private account of Berat Albayrak, Turkey’s energy minister and Erdogan’s son-in-law.

(This version of the story corrects to remove reference to Erdogan quote “Thank God” that was not related to arrest in paragraph 13)

(Additional reporting by Michelle Martin in Berlin; writing by David Dolan; editing by Jason Neely and Keith Weir)